The present invention relates generally to an apparatus for guiding elevator cars and, in particular, to an apparatus for preventing transmission of guide alignment errors and an unintended engagement of the car arresting device.
Guide alignment errors usually are horizontal deviations from a vertical line generally parallel to the path of travel of an elevator car. In the case of column-like guides formed by extruded profiles, another type of alignment error can arise. Due to the manufacturing method, in particular for guide lengths of, for example, 5 to 6 meters, slight twists of a few degrees of angle about the guide axis are difficult to avoid. In consequence of the high stiffness and under consideration of the mode of installation used for this type of guide, it is not possible to reverse such a twist. It follows that elevator car guide devices for this type of guide must have a certain mobility in order to be able to accurately follow the guide path.
The Swiss Patent No. 386 651 shows a slide guide shoe which is carried in a ball socket and, due to this manner of mounting, has additional degrees of freedom for adaptation movements along a twisted guide path.
However, the principle of mounting by means of ball socket is not usable for guide rollers which encompass a column-like guide because the center of rotation of the car mounted guide equipment lies outside the guide cross-section and because this form of mounting has too many degrees of freedom for tracking movements for per se absolutely straight guides.
For the engagement of a conventional arresting device mounted on an elevator car, column-like guides include a projecting vertically extending brake leg. In the case of twist errors of the guide about its longitudinal axis, the leg could contact the arresting device and thus cause an unintended engagement of the same. To provide a greater air gap between an arresting device brake wedge and a brake surface on the guide as a countermeasure to unintended engagement is only conditionally possible due to the limited brake wedge travel and thus only partially solves the problem.
The U.S. Pat. No. 5,159,995 shows an elevator car wedge arresting device with two guide rollers. The two sprung guide rollers are firmly connected with the arresting device and have a limited spring travel which is less than the air gap between the brake wedge and the brake surface on the guide.
With this equipment, the air gap between the brake wedge and the brake surface must be dimensioned to be relatively large, because the spring travel of the guide rollers must be accommodated therein. An undesired reaction delay upon the triggering of the arresting device always results from this configuration. Moreover, a new arresting device must be constructed or an existing one rebuilt expensively.